This proposal requests funds to purchase a Beckman Model XL-I analytical ultracentrifuge. This instrument is needed to support a wide variety of ongoing research projects (4 major and 5 minor user groups) within the interdepartmental Biochemistry Program at Indians University, Bloomington. These projects involve the analysis of structural and/or binding characteristics of proteins, peptides, and nucleic acids. The analytical ultracentrifuge will be used to investigate the following systems in the major user groups: chemokines and glyoxalase I (Martin Stone); complexes of RNA and viral regulatory proteins (Andrew Ellington); factors involved in regulation of cellular differentiation (Yves Brun); and steroid receptors (Peter Cherbas). Systems that will be investigated by the minor user groups include: protein-phospholipid interactions (David Daleke); translation initiation factors (Thomas Donahue); coiled-coil peptide and protein-phospholipid complexes (Martha Oakley); transcription termination factor Rho bound to RNA (John Richardson); and RNA and protein targets for X-ray crystallography (William Scott). The need for this instrument is immediate. Two groups have obtained preliminary analytical ultracentrifuge data at other institutions and several others have prepared samples ready for the proposed analytical ultracentrifuge experiments. This request is strongly supported by the Departments of Chemistry and Biology and the Indiana Molecular Biology Institute. The instrument will complement other sophisticated analytical techniques in these departments and will further strengthen the rapid development of structural biology research at Indiana University. The instrument will be located in the Chemistry Department and will be made available to the local research community. A detailed plan is presented for training and supervising users and ensuring appropriate maintenance of the instrument.